This invention relates to a valve of the flow-shut off type, comprising a valve member adapted to be moved relative to a valve seat for varying the size of a first passage; means for defining a second passage of the valve in series with the first passage, which second passage is so oriented that the flow therethrough occurs radially from within to without; wherein the means defining said second passage comprise a primary member provided with at least one aperture, as well as a secondary member connected to the valve member, which secondary member is adapted to be moved with said valve member for variably clearing or shutting off said at least one aperture; and wherein means are provided for reducing the sound produced by the valve.
Such a valve is known from French patent publication 2,382,639 (hereinafter referred to as the French patent publication).
The invention also relates to a valve of the flow-opening type.
Hereinafter, the general term "valve" denotes a shut-off valve or control valve, for example. Such a valve may be mounted in a transmission pipe for a liquid or gaseous medium, and serves, for example, for opening or shutting off the pipe, as desired, or for controlling the rate of flow in the pipe while maintaining a fixed pressure on the inlet side or on the outlet side, or a variable pressure on the inlet side and on the outlet side, such that requirements as regards the service of the valve are satisfied. In general, in operation the valve is opened to a greater or lesser extent, with the medium flowing through the passage of the valve under the influence of the pressure difference across this passage. The pressure on the inlet side and on the outlet side of the valve may be determined by external factors, and may therefore be fixed. In the case of transmission of natural gas, for example, the valve may be mounted as a separation between a regional distribution network and an urban network, in which prevail pressures of 40 bara and 8 bara, respectively.
It is well known that in the immediate vicinity of the passage of the valve, very high flow rates may occur as a result of which a very great deal of noise may be produced. In order to reduce the sound load on the surroundings, the known valve is provided with means that partly absorb the sound energy produced in the valve so as to limit the level of the sound emitted to the surroundings. In the known valve, these means have the form of superposed rings of such a form that the fluid, when passing the rings, traverses a curvy path from within to without; these rings being referred to in the French patent publication as "chicanes".
A first disadvantage thereof is that the sound is only damped when it has already been produced.
A further disadvantage is that the free passage of the rings is particularly small, so that they have a reductive influence on the capacity of the valve. In point of fact, in practice this means that in order to obtain in the known valve certain characteristics as regards regulatory capacity, primary pressure, secondary pressure and rate of flow, the entire valve, i.e. the combination of valve member, primary member, secondary member and sound-absorbing rings, must be designed for such characteristics. Already many valves not as yet provided with sound-reducing means are used, in which the noise caused by high flow rates has been accepted so far. However, there is a need for these existing valves to be adapted so as to meet increasingly stricter environmental requirements as regards sound-production, while, of course, the original characteristics of the valve must be maintained or changed only to a very limited extent. This is not possible with the rings referred to: either only a minor sound-damping effect is attained with an acceptable deviation from the original characteristics or an acceptable sound-damping effect is attained with an unacceptable deviation from the original characteristics.